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[SVC36-P13] Estimation of yield strength and formation temperature of Man Jang Gul
Keywords:lava tube, yield strength, lava flow, lava temperature
[Introduction]
Man Jang Gul [1-4], located in the northeastern part of Jeju Island, shown in Figures 1-3, is a lava tube cave with a total length of 8.9 km and with a partially multi-layered lava tube cave. This is a large-scale lava tube cave system with a maximum width of 23m and a maximum cavity height of 30m(Photo 1). Here, the yield strength of lava was obtained from the height and inclination angle of Man jang gul Cave, then, the lava temperature when the cave was formed was estimated.
[Estimation of lava yield strength and lava temperature]
Formula fB= R(ρgsinα)/2 to obtain the yield strength indicating the critical flow condition [5] inside the tube (H=2R) from the average inclination angle α of the tubular cavern: 0.4 degrees and the maximum cavity height H: 30m,with ρ=2500kg/m3, g=9.8m/sec2, gives fB=1282.6Pa.
Although there is no temperature dependence data for the yield strength of the lava of Man jang gul, the temperature was estimated here by using the temperature dependence formula for the basaltic lava yield strength obtained elsewhere [6]. (a) Mt. Mihara 1951 lava temperature dependent yield strength: log10fB=12.67-0.0089θ (where θ is temperature in degrees Celsius and fB is in Pa), θ=1074°C, (b) Etna lava temperature dependent yield strength: log10fB= 34.1836-0.0289θ, (θ is Celcius, unit of fB is Pa), θ=1075.4℃, (c) Lava temperature dependent yield strength of Mt. Fuji: log10fB = 27.533-0.0229θ, (θ is Celcius, unit of fB is Pa), θ = 1066.6℃.
[About multi-level cave (tube-in-tube)]
As you can see in Photo 2, there is an example of a lava tube cave being formed inside the cave. This is an example of a lava tube cave (secondary cave) (photo 2) formed by reflowing lava into a previously formed cave (primary cave) (photo 1). The height of the second cave is lower than that of the first cave. Since it is lower than that of the first cave, the lava temperature at the time of formation is higher than that of the first cave.
[Summary]
We estimated the yield strength and temperature of the lava flow that formed Man Jang Gul, Jeju Island. The obtained yield strength and estimated temperature are estimated to be fB = 1283 Pa and θ = 1067-1075°C, which are considered reasonable values compared with other examples of basaltic lava.
It seems that tube-in-tube formation temperatures are a little bit higher.
References:
[1] Takanori Ogawa (1985): Jeju Lava Cave, Korean Culture 7-5
[2] Takanori Ogawa (1988): Lava Caves in Jeju Island, South Korea, Dongjin, Vol. 7, No. 4, Japan Cave Association
[3] Hong Si-Hwan (1988): Caves on Jeju Island, Rissho University Japan-Korea Joint Academic Research Team on Jeju Island, Korea Jeju Island Regional Research Survey Report
[4] Teruhiko Sameshima, Takanori Ogawa, and Naruhiko Kashima (1988): Fifth International Symposium on Vulcanospeleology, Excursion Guide Book
[5] Tsutomu Honda (2001): B10 Mechanism of Formation of Mt.Fuji Lava Cave and Knowledge Obtained, Proceedings of Volcanological Society of Japan,2001
[6] Tsutomu Honda, Junichi Haruyama (2020): 3E11 Identification method of lava flow temperature during Earth-Moon lava tube cave formation, 64th Space Science and Technology Conference
Man Jang Gul [1-4], located in the northeastern part of Jeju Island, shown in Figures 1-3, is a lava tube cave with a total length of 8.9 km and with a partially multi-layered lava tube cave. This is a large-scale lava tube cave system with a maximum width of 23m and a maximum cavity height of 30m(Photo 1). Here, the yield strength of lava was obtained from the height and inclination angle of Man jang gul Cave, then, the lava temperature when the cave was formed was estimated.
[Estimation of lava yield strength and lava temperature]
Formula fB= R(ρgsinα)/2 to obtain the yield strength indicating the critical flow condition [5] inside the tube (H=2R) from the average inclination angle α of the tubular cavern: 0.4 degrees and the maximum cavity height H: 30m,with ρ=2500kg/m3, g=9.8m/sec2, gives fB=1282.6Pa.
Although there is no temperature dependence data for the yield strength of the lava of Man jang gul, the temperature was estimated here by using the temperature dependence formula for the basaltic lava yield strength obtained elsewhere [6]. (a) Mt. Mihara 1951 lava temperature dependent yield strength: log10fB=12.67-0.0089θ (where θ is temperature in degrees Celsius and fB is in Pa), θ=1074°C, (b) Etna lava temperature dependent yield strength: log10fB= 34.1836-0.0289θ, (θ is Celcius, unit of fB is Pa), θ=1075.4℃, (c) Lava temperature dependent yield strength of Mt. Fuji: log10fB = 27.533-0.0229θ, (θ is Celcius, unit of fB is Pa), θ = 1066.6℃.
[About multi-level cave (tube-in-tube)]
As you can see in Photo 2, there is an example of a lava tube cave being formed inside the cave. This is an example of a lava tube cave (secondary cave) (photo 2) formed by reflowing lava into a previously formed cave (primary cave) (photo 1). The height of the second cave is lower than that of the first cave. Since it is lower than that of the first cave, the lava temperature at the time of formation is higher than that of the first cave.
[Summary]
We estimated the yield strength and temperature of the lava flow that formed Man Jang Gul, Jeju Island. The obtained yield strength and estimated temperature are estimated to be fB = 1283 Pa and θ = 1067-1075°C, which are considered reasonable values compared with other examples of basaltic lava.
It seems that tube-in-tube formation temperatures are a little bit higher.
References:
[1] Takanori Ogawa (1985): Jeju Lava Cave, Korean Culture 7-5
[2] Takanori Ogawa (1988): Lava Caves in Jeju Island, South Korea, Dongjin, Vol. 7, No. 4, Japan Cave Association
[3] Hong Si-Hwan (1988): Caves on Jeju Island, Rissho University Japan-Korea Joint Academic Research Team on Jeju Island, Korea Jeju Island Regional Research Survey Report
[4] Teruhiko Sameshima, Takanori Ogawa, and Naruhiko Kashima (1988): Fifth International Symposium on Vulcanospeleology, Excursion Guide Book
[5] Tsutomu Honda (2001): B10 Mechanism of Formation of Mt.Fuji Lava Cave and Knowledge Obtained, Proceedings of Volcanological Society of Japan,2001
[6] Tsutomu Honda, Junichi Haruyama (2020): 3E11 Identification method of lava flow temperature during Earth-Moon lava tube cave formation, 64th Space Science and Technology Conference